The present disclosure relates to display devices, and more particularly, to a display device capable of displaying a so-called naked-eye stereoscopic image.
A variety of stereoscopic image display devices that realize a stereoscopic view by allowing a viewer to observe two images with parallax have been known from the related art. Methods employed in the stereoscopic image display devices are largely classified into two categories: a glasses method in which a parallax image is separately input to the viewer's respective left and right eyes through his glasses, and a naked-eye method (glasses-free system) in which a parallax image is input to both the left and right eyes without using glasses. As an example of the naked-eye stereoscopic image display devices, a lenticular stereoscopic image display device and a parallax barrier stereoscopic image display device are being put into practical use. The lenticular stereoscopic image display device includes a transmissive display panel (two-dimensional image display device) in combination with a lenticular lens. The parallax barrier stereoscopic image display device includes a transmissive display panel in combination with a parallax barrier.
The parallax barrier stereoscopic image display device typically includes a transmissive display panel and a parallax barrier (for example, see Japanese Patent Application Laid-Open Publication No. 2005-086056). Specifically, the transmissive display panel has a plurality of pixels arranged in the horizontal direction (lateral direction) and vertical direction (longitudinal direction) to form a two-directional matrix pattern. The parallax barrier has a plurality of light-transmissive portions and light-shielding portions extending generally in the vertical direction to be juxtaposed alternately in the horizontal direction. The transmissive display panel is often composed of liquid crystal display devices and is illuminated by a planar illumination device from its back face, and each pixel operates as a type of an optical shutter. When a color display is performed on the transmissive display panel, one pixel is typically composed of a plurality of sub-pixels, each sub-pixel being surrounded by black matrix.
However, the light-transmissive portions of the parallax barrier and the black matrix of the transmissive display panel have their respective regular repeated patterns. Thus, moire may occur when the parallax barrier and the transmissive display panel are juxtaposed. FIG. 25 illustrates a photograph showing a state where the moire is occurred in a display device in the related art. The moire can be classified into two categories: a moire caused by the shape of light-transmissive portion in the parallax barrier and the shape of black matrix in the transmissive display panel (hereinafter referred to as “shape-induced moire” for convenience), and a moire caused by the diffraction of light (hereinafter referred to as “diffraction-induced moire” for convenience).
The cause why the shape-induced moire is occurred will be explained with reference to FIGS. 23A, 23B, 24A and 24B which schematically illustrate an arrangement relationship between the transmissive display panel and the parallax barrier. Note that in these figures the transmissive display panel and the parallax barrier are illustrated to be overlapped with each other for convenience. Further, narrow cross-hatched lines slanting from top left to bottom right are drawn on an area where a light-transmissive portion 131 or 531 in the parallax barrier is projected onto the transmissive display panel. Furthermore, intermediate-sized cross-hatched lines slanting from top right to bottom left are drawn on an area where a light-shielding portion 132 or 532 in the parallax barrier is projected onto the transmissive display panel. Moreover, wide cross-hatched lines slanting from top left to bottom right are drawn on an area where the light-shielding portion 132 or 532 is overlapped with the transmissive display panel. This will be similar to FIG. 14 to be described later. Each pixel is surrounded by black matrix.
In this regard, in a case where a width of the light-transmissive portion 131 in the parallax barrier along a first direction is equal to a pitch ND of a sub-pixel array along the first direction (see FIG. 23A), even if a viewpoint of a viewer observing an image is slightly shifted to the first direction (see FIG. 23B), there is no change in size of the pixel area that is not covered with the light-shielding portion 132. Thus, even if the viewpoint of a viewer observing an image is slightly sifted to the first direction, there is no change in the brightness of the screen. Therefore, the moire is not generated.
On the other hand, in a case where a width of the light-transmissive portion 531 in the parallax barrier along the first direction is not equal to the pitch ND of a sub-pixel array along the first direction (see FIG. 24A), when the viewpoint of a viewer observing an image is slightly shifted to the first direction (see FIG. 24B), there is a change in size of the pixel area that is not covered with the light-shielding portion 532. Thus, when the viewpoint of a viewer observing an image is slightly sifted to the first direction, there is a change in the brightness of the screen. As a result, the moire is generated.